Computer systems typically include expansion connectors for the addition of peripheral devices to extend and enhance the function of the computer system. Examples of such peripheral devices include modems, network cards, adapter cards, Compact Discs (CD's), and Digital Video Discs (DVD's) drives, Random Access Memory (RAM), data storage devices, and sound devices. Such peripheral devices are typically formed in accordance with an industry standard specification that governs the physical connection to the computer system through a data port or slot, and the data bus over which communications with the peripheral device are conducted.
Some industry standard specifications allow for the insertion and removal of the peripheral devices while the computer system is running without damaging the computer system or peripheral device. This “hot swapping” of the peripheral device is particularly desirable in computer systems that are required to operate continuously, such as communication network controllers, servers, gateways, routers, and the like. One such industry standard specification is the Peripheral Component Interconnect Express (PCI-X) specification. Like its predecessor, the Peripheral Component Interconnect (PCI) specification, the PCI-X specification enables high-speed communication between compatible peripheral devices and the central processing unit (CPU) of the computer system. In a PCI-X device pair, data is communicated between a transmitter of one PCI-X device and a receiver of another PCI-X device over a transmission line, to which data port terminations of the transmitter and receiver are capacitively coupled.
The hot swapping function accommodated by the PCI-X specification makes it necessary for a transmitter of one PCI-X device to check to determine whether the corresponding receiver of the peripheral device it wishes to communicate with is present. This is accomplished by periodically performing a receiver detect function. The receiver detect function generally involves comparing a voltage at the data port termination of the transmitter to a reference voltage. The corresponding receiver is determined to be present when the voltage at the data port is above the reference voltage after a predetermined period of time.
Additionally, it is necessary to provide protection from electrostatic discharge (ESD) where static charge builds on the transmission line and is discharged through a peripheral device when it is connected to the transmission line. This discharge could be large and could damage the peripheral components. One manner in which ESD protection is provided is by switching the termination of the data port of the transmitter into a high impedance state, once it is determined that the receiver is absent, to reduce the magnitude of the discharge that could occur when the receiver is reconnected. Unfortunately, this ESD protection scheme can give rise to high amplitude noise at the high impedance data port termination of the transmitter, which can interfere with the implementation of the receiver detect function. As a result, false detections of the receiver can occur resulting in data miscommunications.